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United States Patent ELEC'IROCHENHCAL MANUFACTURE OF HALOHYDRINS Robert W. Foreman, Cleveland, Lorraine S. Szabo, Chagrin Falls, and Franklin Veatch, Lyndhurst, Ohio, assignors to The Standard Oil Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Filed Dec. 29, 1958, Ser. No. 783,175

8 Claims. ((1204-81) The present invention relates to the preparation of halogenated organic hydroxy compounds, and particularly to the manufacture of aliphatic halohydrins. More specifically, the invention pertains to a novel process whereby halohydrins may be effectively and economically produced from unsaturated aldehydes and ketones and preferably from a,B-unsaturated aliphatic aldehydes having at least some solubility in water. In a specific embodiment, the present invention covers a process of electrolytically treating a. dilute aqueous solution of an aliphatic unsaturated aldehyde and a hydrogen halide. to produce high yields of the corresponding halohydrins. The process has particular utility in the manufacture of halohydirns from acrolein.

The prior art has disclosed several processes for the electrochemical treatment of unsaturated compounds. Of particular interest are the disclosures relating to the production of halohydrins from mfimnsaturated alcohols. Halohydrins are produced according to such processes by subjecting a dilute aqueous mixture of unsaturated alcohol and hydrogen halide to the action of a direct electric current. In the case where glycerin mono-halohydrin is the. desired product, allyl alcohol is the preferred starting material. The prior art also suggests that allyl alcohol may be produced by the electrolytic reduction of acrolein. This reaction is accomplished by subjecting acrolein to the cathodic reducing action of a direct current in a medium comprising sulphuric acid, ferrous sulphate, and zinc acetate. The present invention represents a considerable advance over the processes of the prior art since halohydn'ns may now be produced directly form cap-unsaturated aldehydes or ketones, e.g., glycerin halohydrins from acrolein. It appears that the process of this invention involves the simultaneous reduction of the aldehyde group and the halohydrination of the olefinic bond in the molecule.

In brief, the process of this invention is accomplished by subjecting an aqueous solution of an unsaturated aldehyde or ketone to the action of a directelectr-ic current in the presence of certain hydrogen halides. The direct current is conveyed by the cathodic and anodic electrodes disposed or immersed in said solution. Representative examples of the unsaturated carbonyl compounds which may be treated in accordance with the processof the present invention are acrolein, 'methacrolein, crotonaldehyde, methyl vinyl ketone, mesityl oxide, 2-cyclohexenone and the like and their homologs and analogs. In general, we prefer to employ the lower aliphatic carbonyl compounds containing three to eight carbon atoms. It is to be noted that all of the above compounds are water soluble to a greater or lesser extent. I

Although examples givenabove present compounds containing only one unsaturated linkage, it is obvious that aldehydes or ketones which may be treated in accordance with the process of this invention may have a greater number of such unsaturated linkages. Also, the compounds may contain one or more carbonyl radicals. It is to be further understood that the aliphatic and/ or the course of the reaction.

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alicyclic unsaturated compounds of the type presented hereinabove may have various alkyl, aryl, and/ or aralkyl substituents in place of one or more of the hydrogen atoms directly attached to the various carbon atoms of the molecule.

The process of this invention may be effected under widely different conditions depending upon the starting material, the desired halohydrin, etc. These variables will be described hereinbelow with particular reference to the effects thereof on the electrochemical halohydrination of acrolein to produce high yields of glycerin monohalohydrin. It is to be understood, however, that the hereinbelow described variations will also affect to the greater or lesser degree the effectiveness of the electrochemical halohydrination of the other compounds of the defined classes.

When effecting the process of the present invention an undivided electrolytic cell is usually employed since the success of the process depends upon reactions of both the cathode and anode. Accordingly, the divided cells which are employed in most electrolytic processes may be dispensed with in the. present process. The removal of the diaphragm-1s employed to divide conventional cells is advantageous since the resistance of the cell is thereby lowered with a consequent decrease in the power consumtion. Both the cathode and anode may be constructed of any electrically conductive material which is inert to the reactants and the reaction products. Representative materials which may be employed for the manufac ture of the cathode are cadmium, zinc, tin, iron, lead, mercury, or alloys of any of these materials. Cadmium is the preferredcathode material as it seems to give the best results. The anode may be conveniently constructed from materials such as carbon, graphite, platinum and like materials which are not affected appreciably by the conditions of the reaction.

Preferably, the cathodes and anodes should have the same effective area, but it is also possible to employ cathodes and anodes having different effective areas. In order to obtain maximum utilization of the current, it is preferred to have the surface of the cathodes and anodes facing each other and this may be conveniently accomplished by employing flat plates as electrodes. When the apparatus contains morethan one cell the-electrodes are normally arranged so that the distances between the anode and cathode of the respective cells are substantially equal.

In one embodiment of this invention the electrolytic cell employed comprises a plurality of plates which serve as cathodes and anodes and which are alternately arranged so as to provide a sandwich type structure containing a plurality of individual cells comprising both a cathode and an anode. Suitable gaskets are disposed between the various plates in order to prevent leakage of the material in the cell. All of the plates, except the end plates, are provided with openings therein so that the solution of reactants which is introduced into the apparatus will flow through the various cells serially.

Alternately, the reactants may be introduced separately is no limit in the number of cells which may be included in the same apparatus and the number and dimension of these cells will depend principally on the amount of throughput desired. The current densities may vary within relatively wide limits without adversely affecting Generally, it may be stated that the current density should fall somewhere in the range of 10 to 1000 amperes per square foot and arange of 30 to 500 amperes per square foot is preferred. The optimum current density will vary depending upon the operating conditions such as the material to be treated,

concentrations employed, operating temperature, etc. When starting up the process or at other times, it may be desirable to reverse the polarity of the electrodes for a brief period as this seems to improve the activity of the cell. The theory of the mechanism by which the reversal of the polarity causes an improvement in the activity of the cell is not known, but the theory is unimportant to the process of this invention in view of the actual results obtained.

Although it is preferred to operate the process of this invention in a continuous manner, a batch type process is operable and is contemplated within the scope of this invention. In the case of the continuous process the concentration of the a,p-unsaturated aldehyde in the aqueous solution introduced to the electrolytic cell obviously should not exceed the solubility of the aldehyde in the electrolytic solution. In the case of acrolein, the upper limit consequently will be above 20%. However, it is often desirable to operate at lower concentrations such as about 0.01% to about Any halogen selected from the group consisting of chlorine, bromine, and iodine or mixtures of any of these may be employed in this process and of these bromine is preferred. Fluorine does not form a fluorohydrin under the conditions of the process of this invention, but its presence is not excluded as it may be present in admixture with the operable halogens. Ordinarily, the halogen will be introduced to the reaction mixture in the form of an aqueous solution of its hydrogen derivative, i.e., as the hydrogen halide. Soluble halide salts may be employed as a supplemental source of the halogen. Likewise, other electrolytes may be employed to improve the conductivity of the electrolytic solution. Generally speaking, the hydrogen halide should be present in at least an amount sufficient to convert all of the aldehyde present to the monohalohydrin and it is generally desirable to employ an excess of the hydrogen halide since there is usually some formation of the dihalohydrin. Since the process of this invention must be conducted in an acid medium, the introduction of the hydrogen halide insures that the pH of the cell will remain below 7.

The temperature at which the process is conducted is not critical, but generally we prefer to operate at temperatures below the boiling point of the aldehyde or ketone undergoing reaction so that the use of pressure is ob viated. However, operations at super-atmospheric pressure are feasible and they are not to be excluded from this invention.

The desired products of the process are monoand dihalohydrins. In most instances a minor amount of byproduct will be obtained which is usually the saturated derivative of the unsaturated starting material; for example, in the case of acrolein, propionaldehyde and propanol are found as byproducts. The products of the process may be recovered from the aqueous electrolyte solution by conventional means such as distillation or solvent extraction. The unreacted starting materials including the carbonylic starting material and the hydrogen halide may be recovered and recycled to the electrolytic cell. The monoand dihalohydrins which are produced in the process may be hydrolyzed after recovery to the corresponding polyol by conventional means such as heating in the presence of oxides, hydroxides, carbonates and bicarbonates of the alkaline earths or alkali metals, e.g. soda ash, lime, limestone, and caustic soda; In the case where acrolein is the starting material, the product of the hydrolysis will be glycerin.

In preparing the halogenated organic hydroxy compounds according to the present invention, the net result of the interaction of the three reacting bodies; namely, the unsaturated aldehyde or ketone, the hydrogen halide and the water under the influence of the direct electric current is that a hydroxy radical and a halogen atom or two halogen atoms become attached to the olefim'c bond of the starting material to form a halogenated organic hydroxy compound or a halogenated carbonyl compound, and this halohydrination or halogenation is believed to be eifected at or in the substantial vicinity of the anode. At the same time the aldehyde or ketone group attached to the organic starting material is apparently reduced at or in the substantial vicinity of the cathode. The cathode and anode reactions appear to take place simultaneously, but whether the reactions are simultaneous or sequential is not important to this invention. It may well be that there are various intermediate reactions including the formation of a hypohalous acid which precede the formation of the end products, but at this time it is not known definitely just what reactions transpire in the cell. Consequently, the hypothesis offered herein as to the course of the reaction is not to be construed as limiting this invention in any manner.

The term current efliciency or electric current efiiciency as employed herein denotes the ratio of the electricity employed equivalent to the number of mols of substance transformed to the quantity of electricity actually consumed. In the halohydrination of unsaturated aldehydes and ketones according to the present process, a theoretical minimum of 2 faradays of electricity are required to form one mole of halohydrin.

The following examples will serve to illustrate the process of the present invention. The sandwich type electrolytic cell described hereinabove was employed in all of these examples. The cell was made up of 6 rectangular plates measuring 2%" x 8". A Vs" gum rubber gasket was employed to separate the plates. The effective electrode area of each side of the plate was 14 sq. in. and since two outermost sides of the plates are not available the apparatus had a total effective electrode area of 140 sq. in. A feed reservoir and pump were employed to introduce the feed to the apparatus in a continuous manner. The reaction products were removed by a pump at a continuous rate corresponding to the rate of the introduction of the feed. The same apparatus was employed in all of the following examples except that the material employed in the cathode and anode was varied in certain instances as will be evident from the following description.

graphite as the anode material, an 0.5 normal solution of hydrogen bromide containing 2% CdBr to which acrolein was added gradually was introduced at a rate of 375 mL/min. An electric current density of 100 amperes/sq. ft. was passed at about 2.7 volts across the individual cells of the apparatus. The reaction was continued for a period of about 1.5 hrs. during which time a total of about 0.24 mole of acrolein and 0.42 mole of hydrobromic acid were introduced. A total of 1.18 faradays of electricity was passed through the solution. The tem perature was maintained at about40 C. during the reaction. Analysis of the resulting solution showed that it contained predominantly glycerol monoand dibromohydrins. The conversion of acrolein to useful products was 93.4% and the yield of the mixture of monoand dibrohohydrins was 80%. An additional yield of 20% was obtained as propionaldehyde and n-propanol. Current efliciency for conversion of acrolein to bromohydrins was 30.4%.

Example II In an apparatus employing cadmium as the cathode and graphite as the anode material, an 0.5 normal solution of hydrogen chloride to which acrolein was added gradually was introduced at a rate of 375 mL/min. An electric current density of amperes/sq. ft. was passed at about 3.6 volts across the individual cells of the apparatus. The reaction was continued for a period of about 1 hour and 40 minutes during which time a total of about 0.23

mole of acrolein and 0.41 mole of hydrochloric acid were introduced. A total of 1.0 faraday of electricity was passed through the solution. The temperature was maintained at about 45 C. during the. reaction. Analysis of the resulting solution showed that it contained predominantly glycerol monoand dichlorohydrins. The conversion of acrolein was 96.3% and the yield of the mixture of monoand dichlorohydrins was 42%. An additional yield of 14% was obtained as propionaldehyde and n-propanol. Current efliciency for conversion of acrolein to chlorohydrins was 19%.

Example III In an apparatus employing zinc as the cathode and graphite as the anode material, a 2 normal solution of hydrogen bromide to which acrolein was added gradually was introduced at a rate of 375 ml./min. An electric current density of 42 amperes/ sq. ft. was passed at about 2.5 volts across the individual cells of the apparatus. The reaction was continued for a period of about 1.25 hrs. during which time a total of about 0.32 mole of acrolein and 0.23 mole of hydrobromic acid were introduced. A total of 0.95 faraday of electricity was passed through the solution. The temperature was maintained at about 25 C. during the reaction. Analysis of the resulting solution showed that it contained predominantly glycerol monoand dibromohydrins. The conversion of acrolein was 89.5% and the yield of the mixture of monoand dibromohydrins was 42.6%. An additional yield of 6.3% was obtained as propionaldehyde and allyl alcohol. Current efficiency for conversion of acrolein to bromohydrins was 25.3%.

Example IV In an apparatus employing cadmium as the cathode and graphite as the anode material, an 0.5 normal solution of hydrogen iodide to which acrolein was added gradually was introduced at a rate of 375 ml./min. An electric current density of 40 amperes/ sq. ft. was passed at about 2 volts across the individual cells of the apparatus. The reaction was continued for a period of about one hour during which time a total of about 0.29 mole of acrolein and 0.10 mole of hydroiodic acid were introduced. A total of 0.75 faraday of electricity was passed through the solution. The temperature was maintained at about 36 C. during the reaction. Analysis of the resulting solution showed that it contained predominantly glycerol monoand di-iodohydrins. The conversion of acrolein was 84.8% and the yeld of the mixture of monoand diiodohydrins was 62%. An additional yield of about 20% was obtained as propionaldehyde and allyl alcohol. Current efiiciency for conversion of acrolein to iodohydrins was 41.3%.

Example V In an apparatus employing cadmium as the cathode and graphite as the anode material, an 0.6 normal solution of hydrogen bromide to which methacrolein was added gradually was introduced at a rate of 760 mL/min. An electric current density of 100 amperes/ sq. ft. was passed at about 3.2 volts across the individual cells of the apparatus. The reaction was continued for a period of about 1.25 hours, during which time a total of about 0.17 mole of methacrolein and 0.25 mole of hydrobromic acid were introduced. A total of 0.93 faraday of electricity was passed through the solution. The temperature was maintained at about 33 C. during the reaction. The conversion of methacrolein to bromohydrins was 78.7%. The current efficiency for the conversion of methacrolein to the corresponding bromohydrins was 29.2%.

Example 1 VI In an apparatus employing cadmium :as the cathode and graphite as the anode material, an 0.65 normal solution of hydrogen bromide to which crotonaldehyde was added gradually was introduced at a rate of 760 ml./min. An electric current density of amperes/sq. ft. was passed at about 2.9 volts across the individual cells of the apparatus. The reaction was continued for a period of about 1.25 hours during which time a total of about 0.20 mole of crotonaldehyde and 0.23 mole of hydrobromic acid were introduced. A total of 0.93 faraday of electricity was passed through the solution. The temperature was maintained at about 33 C. during the reaction. The conversion of crotonaldehyde to the corresponding bromohydrins was 29.8% and the current efiiciency for this conversion was 19.2%.

It is apparent from the above examples that many modifications of the process may be made without departing from the spirit or scope of this invention. The modifications may include variations in the current density, electrolyte concentration, electrode composition, and the like. This application for Letters Patient is intended to include all such modifications which would reasonably be construed to fall within the scope of the appended claims.

We claim:

1. A process for the manufacture of halohydrins which comprises subjecting an aqueous solution of an a,,B-unsaturated carbonylic compound to the action of a direct electric current in an electrolytic cell in the presence of a hydrogen halide selected from the group consisting of hydrogen chloride, hydrogen bromide, and hydrogen iodide.

2. A process for the manufacture of halohydrins which comprises subjecting an aqueous solution of an a,;3-unsaturated carbonylic compound selected from the group consisting of the lower aliphatic aldehydes and ketones to the action of a direct electric current in an undivided electrolytic cell in the presence of a hydrogen halide selected from the group consisting of hydrogen chloride, hydrogen bromide, and hydrogen iodide.

3. A process for the manufacture of glycerin halohydrins which comprises subjecting an aqueous solution of acrolein to the action of a direct electric current in an undivided electrolytic cell in the presence of a hydrogen halide selected from the group consisting of hydrogen chloride, hydrogen bromide, and hydrogen iodide.

4. A process for the manufacture of glycerin halohydrins which comprises subjecting an aqueous solution of acrolein to the action of a direct electric current in an undivided electrolytic cell in the presence of hydrogen bromide.

5. A process for the manufacture of glycerin halohydrins which comprises subjecting an aqueous solution of acrolein to the action of a direct electric current in an undivided electrolytic cell in the presence of hydrogen chloride.

6. A process for the manufacture of glycerin halohydrins which comprises subjecting an aqueous solution of acrolein to the action of a direct electric current in an undivided electrolytic cell in the presence of hydrogen iodide.

7. A process for the manufacture of glycerin halohydrins which comprises subjecting an aqueous solution of acrolein to the action of a direct electric current in an undivided electrolytic cell in which the cathode surface comprises cadmium and the anode surface comprises graphite in the presence of a hydrogen halide selected from the group consisting of hydrogen chloride, hydrogen bromide, and hydrogen iodide.

8. A process for the manufacture of glycerin halohydrins which comprises subjecting an aqueous solution of acrolein to the action of a direct electric current in an undivided electrolytic cell in which the cathode surface comprises cadmium and the anode surface comprises 2,124,851 graphite in the presence of hydrogen bromide. 2,282,683 r 2,462,301

References Cited in the file of this patent UNITED STATES PATENTS 552 319 1,253,615 McElroy 1 Jan. 15, 1918 8 Fitzky July 26, 1938 Tamele et a1. May 12, 1942 Bludworth et a1. Feb. 22, 1949 FOREIGN PATENTS Great Britain Apr. 1, 1943 

1. A PROCESS FOR MANUFACTURE OF HALOHYDRINS WHICH COMPRISES SUBJECTING AN AQUEOUS SOLUTION OF AN A,B-UNSATURATED CARBONYLIC COMPOUND TO THE ACTION OF A DIRECT ELECTRIC CURRENT IN AN ELECTROLYTIC CELL IN THE PRESENCE OF A HYDROGEN HALIDE SELECTED FROM THE GROUP CONSISTING OF HYDROGEN CHLORIDE,HYDROGEN BROMIDE, AND HYDROGEN IODIDE. 